Necrotic ring spot (Leptosphaeria korrae)

What does it look like?

This disease is unmistakable, with large rings, often a foot or larger, filled in with dead, brown grass. Its favorite hosts are Kentucky bluegrass and fine fescue turf.

When is a lawn susceptible?

This disease sets in during the cool, wet weather of spring or fall. The large rings form during hot, dry summers. If your lawn is close to a wooded area, its more susceptible to necrotic ring spot. And while it favors sodded lawns, it has been known to attack seeded lawns as well. One positive trait is that the severity of this disease decreases in lawns older than five years, so lawn maturity strengthens immunity.

How can we get rid of it?

Unfortunately, this disease has to run its course once it has appeared. Because it is a soil-born disease, growth must be kept active, but in a subtle fashion. To minimize the symptoms, maintaining proper lawn moisture levels is essential. Daily watering for about 10 minutes can help considerably, provided you start this in early summer with previously infected areas. Another effective measure is the use of slow release fertilizers, which provide root stimulation during the warm months. Regardless, do not replant dead areas with patch kits that contain ryegrass - this will actually stimulate the spread of the disease! Fungicides really don't affect this disease, so dig in and let it run its course, following the steps and keeping your lawn as strong as possible.